Air carrier made unauthorized descent below assigned altitude resulting in less than standard separa...

Attributes
ACN	127285
Time
Date	198911
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : sea
State Reference	WA
Altitude	msl bound lower : 12600 msl bound upper : 13000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	descent other
Route In Use	arrival other enroute airway : sea
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Transport, High Wing, 2 Turboprop Eng
Flight Phase	cruise other
Route In Use	arrival other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Experience	controller radar : 20 flight time last 90 days : 15 flight time total : 500 flight time type : 350
ASRS Report	127285
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : overshoot conflict : airborne less severe non adherence : required legal separation non adherence : clearance
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	controller : issued new clearance
Consequence	Other
Miss Distance	horizontal : 0 vertical : 600
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Working air carrier X in level flight assigned 13,000. Air carrier Y underneath at 12,000 in level flight. I was working several other aircraft at same time. Conflict alert went off as it does all the time (crying wolf) so I scanned all traffic. Three targets overlapped and when I swung data blocks around, air carrier X was coming down right on air carrier Y. I keyed microphone, and said 'get back to one three thousand'. Pilot turned mode C off and when it came back on, the aircraft was level 13,000. Informed supervisor of loss of separation. No paperwork filed. We all know what would have happened had it been a TCA violator or controller's mistake. Where's the credibility anymore?

Original NASA ASRS Text

Title: ACR MADE UNAUTH DESCENT BELOW ASSIGNED ALT RESULTING IN LESS THAN STANDARD SEPARATION.

Narrative: WORKING ACR X IN LEVEL FLT ASSIGNED 13,000. ACR Y UNDERNEATH AT 12,000 IN LEVEL FLT. I WAS WORKING SEVERAL OTHER ACFT AT SAME TIME. CONFLICT ALERT WENT OFF AS IT DOES ALL THE TIME (CRYING WOLF) SO I SCANNED ALL TFC. THREE TARGETS OVERLAPPED AND WHEN I SWUNG DATA BLOCKS AROUND, ACR X WAS COMING DOWN RIGHT ON ACR Y. I KEYED MICROPHONE, AND SAID 'GET BACK TO ONE THREE THOUSAND'. PLT TURNED MODE C OFF AND WHEN IT CAME BACK ON, THE ACFT WAS LEVEL 13,000. INFORMED SUPVR OF LOSS OF SEPARATION. NO PAPERWORK FILED. WE ALL KNOW WHAT WOULD HAVE HAPPENED HAD IT BEEN A TCA VIOLATOR OR CTLR'S MISTAKE. WHERE'S THE CREDIBILITY ANYMORE?

Data retrieved from NASA's ASRS site as of August 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Air carrier made unauthorized descent below assigned altitude resulting in less than standard separation.